I don't know what historical securities are but i know how Experian works and how the results can mean in decline for credit . Check your experian file and check all addresses going back 6 years, you must also check anyone who have had a financial relationship with in the last 6 years too. People quite often look at their file and think its clear, but lurking at an address several years back is an ex-partner/friend will a bad credit history. If you do find associated adverse you will need to get 'unassociated' then experian will update your file. Hope this helps.